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Value Extraction from Ferrochrome Slag: A Thermochemical Equilibrium Calculation and Experimental Approach
No full textThe valorization of slag from the production of high-carbon ferrochrome is a challenge for ferrochrome producers. The recycling of high-carbon ferrochrome slag was explored through the smelting route to recover Fe-Si-Al-Cr alloys and reengineer the residual slag for alumina-enriched refractory material. In this research, the focus was to reduce the SiO2% and enrichment of Al2O3% in the final slag and recover the metallic value in the form of a complex alloy containing Fe, Si, Cr and Al. The manuscript consists of a thermochemical simulation of the smelting of FeCr slag followed by smelting experiments to optimize the process parameters such as temperature and the addition of coke, cast iron and alumina. An experimental investigation revealed that the maximum recovery of Si (57.4% recovery), Al in the alloy (20.56% recovery) and Al2O3 (85.78% recovery) in the slag was achieved at a charge mix consisting of 1000 g of FeCr slag, 300 g of alumina, 200 g of cast iron and 300 g of coke. The present study also demonstrated the usefulness of prior thermochemical calculations for smelting metallurgical wastes such as slag from high-carbon ferrochrome production for value creation and reutilization purposes
Degradation Mechanism of Piezoresistive Sensors Under the Influence of γ -Ray Irradiation
No full textMicro-electromechanical systems (MEMS) technology-based piezoresistive technique is a highly matured transduction technique. It is very popular for the MEMS devices used in various industries such as automotive, process control, aerospace and avionics, consumer electronics, nuclear power plants, and many more. MEMS pressure sensors are one among them, and their deployment in nuclear power plants and aerospace are prominently increasing. Hence radiation-induced performance degradation of piezoresistive pressure sensors has been carried out, which is a prime concern for such industries. Therefore, a set of experiments for the investigation of irradiation-driven performance degradation of MEMS pressure sensors are performed under varying doses of gamma radiations. An insignificant change in sensitivity was recorded which degraded up to a maximum of 0.78%, while the linearity remained unchanged for a cumulative dose of 27.90 Mrad. However, the deviation in the offset voltage of the Wheatstone bridge (WB) configuration was significant and as recorded was 139% at a cumulative dose of 27.90 Mrad. This article explains the degradation mechanism of MEMS piezoresistive sensors using the experiments and TCAD simulations
Structure-Property Correlation of Gravity Die-Cast and Rheocast Al-Mg-Sc-Zr in situ Nano-TiB2 Composite
No full textThe present study investigates the structure-property relationship of gravity die-cast and rheocast in situ processed 1wt%TiB2/Al-3.5Mg-0.15Sc-0.075Zr composites. The reinforcement was synthesized via the reaction of fluoride salts (K2TiF6 and KBF4) in the melt at 750 degrees C for an hour. The cooling slope technique was used for rheocasting, wherein the melt (pouring temperature of 700 degrees C) was allowed to flow over the cooling slope at an angle of 60 degrees. Thereafter, all samples (gravity die-cast and rheocast) were aged at 300 degrees C for 5 h. Microstructural characterization, hardness measurements, tensile tests, and fractography were necessary supplements to this investigation. The results obtained from this investigation infer: (a) The presence of nano-TiB2 particles increases the ductility (15%) of the gravity die-cast specimens; (b) rheocasting increases the strength of the specimen due to transformation from dendritic to equiaxed dendritic morphology and uniform particle distribution (reduced agglomeration). (c) Rheocast and aged specimens show maximum strength and adequate ductility due to the combined effects of structure refinement, reduced agglomeration, and the formation of fine precipitates
Role of Nb (C, N) and Cr carbides on the fracture behavior of Super304H steel using in-situ tensile studies
No full textThe present work investigates the role of Nb (C, N) precipitates and Cr-carbides on the high-temperature fracture behavior of Super304H steel. To accomplish this, both as-received and sensitized steels were subjected to in-situ tensile testing at 650 degrees Celsius. Both samples exhibit the formation of primary cracks along the coarse (>3 mu m) Nb (C, N) precipitates and their decohesion. Additionally, in sensitized samples, Cr-carbides embrittle the grain boundaries resulting in reduced ductility (36 %) and toughness (39 %). Moreover, fine cracks initiation/propagation along the grain boundary Cr-carbides (typically a weaker region in sensitized steels) is observed
Validation of Bromide Leaching through Response Surface Methodology and Separation of Gold from Waste Printed Circuit Boards
No full textThe daily consumption of gold is increasing worldwide; however, its availability from conventional ores is reducing. Alternatively, the presence of gold in waste electrical and electronic equipment (WEEE) is nearly 100 times higher than in natural ore. Therefore, the possibility of the recovery and separation of gold from waste printed circuit boards of obsolete mobile phones is studied in the present work. Initially, the optimization of parameters for the quantitative gold leaching from metal clads of PCBs with halide salts at acidic conditions is studied through response surface methodology. Three factors (parameters), viz. temperature, time and stirring speed are altered during the experiments based on the central composite design (CCD). Leaching parameters have been optimized with the help of the second-order empirical equations and analysis of variance (ANOVA) for maximum gold dissolution. The selective recovery and separation of gold from leach liquor have been achieved with solvent extraction with an organic amide as extractant followed by cementation with zinc powder. The separated gold powder has also been analyzed with XRD and SEM-EDS to check the purity and homogeneous elemental distribution. The statistical design of experiments and separation processes for the effective recovery of gold corroborates the economic feasibility of the proposed process
Valorization of phosphor powder of waste fluorescent tubes with an emphasis on the recovery of terbium oxide (Tb4O7)
No full textWaste fluorescent tubes containing yttrium, europium, lanthanum, cerium, and terbium are considered important resources of rare earths. Due to the scarcity of terbium in natural deposits, phosphor powder from waste fluorescent tubes could be a potential source of terbium. The presence of terbium with stable aluminates matrix in the phosphor powder makes the terbium recovery challenging. The present paper aims to develop a process to recover high pure terbium oxide (Tb4O7) from phosphor powder of waste fluorescent tubes. In the developed process, leach residue obtained after selective leaching of yttrium and europium was treated for the recovery of terbium. The leach residue was treated by alkali roasting-water leaching to break the aluminates and phosphates matrix. Further, La, Ce, and Tb were recovered by HCl leaching. Terbium from lanthanum and cerium was separated by solvent extraction using D2EHPA as an extractant. Various parameters such as extractant concentration, phase ratio, etc. were optimized for the selective extraction of terbium in the organic phase. The counter-current process was simulated for terbium extraction. High pure terbium oxide (99.8%) was produced from the loaded organic by precipitation stripping followed by calcination. The solid residues and final products were characterized by chemical analysis, XRD and SEM-EDS
Role of void nucleation at primary-gamma'/gamma interface on strain softening of nickel-base superalloy 720Li
No full textHigh-temperature tensile deformation behavior of polycrystalline nickel-based superalloy 720Li used for manufacturing aero engine disks was studied by conducting uniaxial tensile tests in the temperature range of 25-800 degrees C and subsequent transmission and scanning electron microscopic examinations to decipher strain hardening/softening behavior. The alloy is strengthened by different sizes of gamma-precipitates named primary, secondary, and tertiary-gamma'. The sizes of primary gamma' is in the range of 0.5-3 mu m and most of them are incoherent with gamma-matrix as confirmed by the TEM study. From engineering stress-strain curves, it was observed that specimens tested in the temperature range of 25-650 degrees C exhibited a significant amount of strain hardening, whereas specimens tested at 720 and 800 degrees C softened after the onset of plastic yielding. From extensive SEM examinations, it is concluded that void nucleation at the primary gamma/gamma interface at 720 and 800 degrees C was the main reason for strain softening after the onset of plastic yielding. Nucleation of voids at primary-gamma'/ gamma interface is ascribed to (i) gamma' size, which loses coherency with the matrix after reaching a critical value (rcrit); and (ii) difference in Schmid factor between gamma' precipitate and gamma matrix, which varies with test temperature. From the misfit data, the rcrit values were calculated at 25 and 800 degrees C and are found to be in the range of 1250-1500 nm and 150-200 nm, respectively. From the electron backscatter diffraction (EBSD) analysis, it is confirmed that at 720 and 800 degrees C when the difference in Schmid factors between gamma' precipitate and gamma-matrix is & 0.1, the probability of formation of the void is high.(c) 2023 Elsevier B.V. All rights reserved
Understanding the Formation Mechanism of Al-Rich Interfacial Layer during Galvanizing of Cu Pre-coated High-Strength Steel Sheet
No full textThis work aims at understanding the formation of a beneficial thin continuous aluminum (Al)-rich interfacial layer with uniform distribution of fine equiaxed Fe-Al crystals formed at the substrate/coating interface during the initial stages of interfacial reactions as well as hindrance of Fe dissolution in Zn layer as soon as copper (Cu) pre-coated high-strength steel substrate is immersed into the molten zinc (Zn) bath containing 0.2 wt.% Al. Pre-coated Cu does not allow the immediate interaction and interdiffusion of Fe and Zn because of the positive heat of mixing between Fe and Cu. As the Cu dissolves in liquid Zn, counter-diffusion of Al and Zn toward the steel interface allows Fe to react with Al and Zn forming the thin Fe-Al inhibition layer with finer equiaxed grains. Moreover, dissolved Cu in the Zn layer would also prevent Fe diffusion in Zn in the time span during dipping, which is beneficial. Atom probe tomography (APT) analysis at the substrate/coating interface location reveals the presence of 56.22 & PLUSMN; 1.36 at.% Al, 35.01 & PLUSMN; 1.31 at.% Fe, 6.33 & PLUSMN; 0.66 at.% Zn, and 0.032 & PLUSMN; 0.01 at.% Cu, similar to the intermetallic compound of Fe2Al(5-x)Znx, as well Cu in the Zn layer supporting the above reasoning
Study on Microstructure-Property Relationship of Inconel 617 Alloy/304L SS Steel Dissimilar Welds Joint
No full textWelding of Inconel 617 (IN617) alloy and austenitic 304L SS steel has been attempted using the autogenous Laser Beam Welding (LBW) process. Characterization of dissimilar weldments was performed on either side of the fusion boundaries. The metallographic results showed that the inhomogeneous microstructure formation for weld metal contained columnar and cellular dendrites near the interface, whilst the columnar, cellular, and equiaxed types of dendrites were in the weld center. The energy dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA) studies revealed the white layer near the interface on both sides of the fusion line, as well as a significant change in the concentration of alloying elements (Fe, Cr, Ni, Co, and Mo). The weld metal accompanied by Cr, Ti, and Mo precipitates evolved in the inter-dendritic spaces. The Cr and Mo-rich M23C6 and Mo-rich M6C phases in IN617 heat-affected zone (HAZ) were found in SEM/EDS and EPMA studies. The 304L SS side showed a distinct HAZ, whilst, on the IN617 side, no distinct HAZ was seen. Samples were prepared from the dissimilar weldments to evaluate their mechanical properties, such as tensile strength and hardness. The microhardness plot showed the non-uniformity in hardness along the weldments. The weld metal hardness was 253 ± 10 HV. The tensile test of the welded joint results was compared with the base metals. The tested results exhibited that the failure of the specimen from 304L SS base metal (BM) or from weld metal with tensile strength was marginally lower than the Inconel 617 base metal but significantly higher than the 304L SS BM. The fracture surface study revealed the presence of Mo and Cr segregation in inter-dendritic spaces, which impoverished the tensile properties. The order of impact toughness was measured as follows: 304L SS BM > 304L SS HAZ > IN617 BM > weld metal > IN617 HAZ. The IN617 HAZ was recognized as the weakest area of the weldments in terms of impact strength. The welded joint was considered safe for AUSC application because the stress-rupture properties were evaluated in between base metals data
Effects of doping iron on the colouring properties of copper chromate pigment
No full textIron-doped copper chromate with (FexCu1-xCr2O4) as a black ceramic decoration pigment is successfully synthesized using a solid-state synthesis method with a pure oxide precursor. The powdered pigment was analysed using X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared analysis, ultra violet-visible and colour-measuring instruments. The calcination temperature was determined from literature at 1350 degrees C for 3 h. The result of the PXRD indicated that the sample contains a spinel structure; moreover, the doping of iron caused the diffractogram peak to shift towards the lower angle due to the small ionic radius of iron compared to the replaced copper. The micrograph of the SEM indicated that the powder particles are well dispersed, and the energy dispersive spectroscopy result confirmed that all samples appear in their purest form. In addition, as the doped iron increases the colour axis of the pigment, L* tends to be more blackish, while the b* value turns more towards blue. However, the intensity of the red colour a* increases till half of the total copper is replaced by the doped iron and the optimal result was achieved which is comparable with commercial black pigment at Fe0.5Cu0.5Cr2O4, having L* = 32.96